Premature Labour

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Premature Labour

In this article

Premature labour may be defined as the presence of contractions of sufficient strength and frequency to effect progressive effacement and dilation of the cervix before 37 weeks of gestation.

Infants born as a result of premature labour have significant morbidity as a result of immaturity. Accurate diagnosis of preterm labour can allow for the prevention or delay of preterm birth where possible and, where this is not possible, earlier provision can be made to provide optimal support for the immature infant.

Epidemiology

Around 52,000 babies were born prematurely in England and Wales in 2012; there has been no change in this figure over a 10-year period.[1]The UK has one of the highest rates of premature births in Europe.[2]

Very premature births occur at less than 32 weeks of gestation. They account for 1.4% of UK births but cause around 51% of infant deaths.

Diagnosis

Pregnant women may present with a history of painful contractions and assume that they are in a premature labour. Many of these women are experiencing Braxton Hicks contractions and over 60% will not have delivered within 48 hours of presentation, many going on to full term.

Additional indications of preterm labour may be gained through history and examination.

History

Length of time that the contractions have been experienced.

Interval between contractions.

Bleeding or amniotic fluid loss.

Previous obstetric history - any previous preterm deliveries.

History of current pregnancy - infections, bleeding, pain, single or multiple fetuses.

Smoking history.

Examination

Speculum examination may reveal dilatation of the cervix and/or amniotic fluid leak through the cervix.

Digital examination:

This should not be performed if it is thought that the membranes have ruptured, as this will increase the risk of infection to the fetus.

If the membranes have not ruptured, however, vaginal examination should be performed, as it is the best way of assessing the onset of premature labour.

Women with intact membranes who are <29+6 weeks of gestation in suspected preterm labour do not require further investigations to confirm this.

For women with intact membranes who are >30+0weeks of gestation:

Transvaginal ultrasound measurement of cervical length is used to estimate likelihood of delivery within the following 48 hours:

If the cervix is >15 mm it is unlikely she is in preterm labour.

Fetal fibronectin is a quick, simple test that may be used as an alternative when transvaginal ultrasound measurement of cervical length is unavailable or unacceptable:

It requires that an internal examination has not been undertaken first.

If fibronectin concentration is ≤50 ng/ml it is unlikely she is in preterm labour.

Vaginal swab - this should be taken in all women with possible premature labour who are being examined, as this will allow appropriate antibiotic therapy to be given if an infection develops at a later stage.

The use of nitrazine sticks is no longer recommended.

Management

Once a diagnosis of premature labour has been made, the priority should be to ensure that the pregnant mother is transported to the safest available facility for delivery of a preterm infant:

If the patient is at home and the labour appears well established, or if the fetus is visualised on examination, a midwife and an ambulance should be summoned.

If the patient is in hospital, the emergency paediatric team should be alerted.

Tocolysis may be considered for women with suspected preterm labour who have had an otherwise uncomplicated pregnancy.

Women most likely to benefit from use of a tocolytic drug are those who are in very preterm labour, those needing transfer to a hospital which can provide neonatal intensive care and those who have not yet completed a full course of corticosteroids.

If the decision is made to use a tocolytic drug, nifedipine is the drug of first choice (unlicensed use); if nifedipine is contra-indicated, offer an oxytocin receptor antagonist (atosiban):[1]

Nifedipine and atosiban seem to have comparable effectiveness in delaying delivery for up to seven days, with fewer maternal adverse effects and less risk of rare serious adverse events than alternatives such as ritodrine or indometacin.

A systematic review and network meta-analysis on trials of tocolytics found that prostaglandin inhibitors and calcium-channel blockers seem to be the best treatment for preterm delivery, on the basis of the four outcomes:

Use of fetal scalp electrodes is not usually recommended below 34+0 weeks of gestation.

Fetal blood sampling is not recommended below 34+0 weeks of gestation

Prognosis

Babies delivered with optimal care after 30 weeks most often survive without any lasting abnormality.

Survival and impairment in early childhood are both closely related to gestational age for babies born at less than 27 weeks of gestation.[8]

A higher proportion of babies admitted for neonatal care now survive without disability, particularly those born at gestational ages 24 and 25 weeks.

Although survival of babies born between 22 and 25 weeks of gestation has increased over a period of two decades, the pattern of major neonatal morbidity and the proportion of survivors affected are actually unchanged.[9]

Preterm birth can have huge psychosocial and emotional effects on the family, as well as being costly for health services.

Prevention

Both intravaginal progesterone and cervical cerclage are used prophylactically to prevent P-PROM in different circumstances. See separate Preterm Prelabour Rupture of Membranes article for more details.

Despite bacterial vaginosis being confirmed as a risk factor for preterm birth and miscarriage, the routine use of antibiotics in women with subclinical infection in preterm labour with intact membranes is controversial. There is evidence that antibiotics given in these circumstances are associated with an increased risk of functional impairment and cerebral palsy in children at age 7.[10]

Article Information

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